ITMI20101988A1 - RUTENIUM-BASED CATALYST AND ITS USE IN THE SELECTIVE HYDROGENATION OF AROMATIC OR POLYINSATURAL COMPOUNDS - Google Patents

Description

Ruthenium-based catalyst and its use in the selective hydrogenation of aromatic or polyunsaturated compounds

The present invention relates to a new ruthenium-based catalyst and its use in the selective hydrogenation of aromatic or polyunsaturated compounds.

More particularly, the present invention relates to a new ruthenium-based catalyst and its use in the selective hydrogenation of aromatic hydrocarbons, for example benzene and / or toluene and xylenes, or of polyunsaturated compounds, for example dienes or carbonyls Î ± , β-unsaturated.

The selective hydrogenation reaction of benzene to cyclohexene, for example, has become part of the panorama of reactions of interest in industrial chemistry due to the importance of this olefin as an intermediate of numerous processes related to the production of polymeric materials.

As is known, the selective hydrogenation reaction of benzene to cyclohexene is a heterogeneous gas / liquid / solid reaction which occurs in the presence of a heterogeneous catalyst essentially consisting of ruthenium supported on an inert and insoluble solid in the reaction medium. The liquid phase is, in turn, composed of two phases, an organic phase and an aqueous phase, the latter favoring the desorption of the cyclohexene from the surface of the catalyst.

In the scientific literature there are numerous documents relating to the preparation of ruthenium-based catalytic systems, suitable for the selective hydrogenation of polyunsaturated compounds. By way of example, US patents 4,734,536 and 5,589,600 can be mentioned which refer to ruthenium catalysts supported on zirconia and the methods for their preparation. These methods, as is known, require a preparation of the catalyst in two stages, the first of which concerns the synthesis of the metal catalyst in powder form, therefore with the isolation and purification of the metals, while the second involves the deposition of the active elements on the inert support.

The Applicant has now found a new ruthenium-based catalyst which has proved particularly active in selective hydrogenation reactions when used with a particular combination of support and promoter elements. Furthermore, the preparation of the catalyst takes place in a single stage instead of in two stages as occurs in the processes described in the prior art.

In the state of the art, there are processes that allow the single-stage preparation of catalytic systems suitable for the selective hydrogenation of polyunsaturated compounds. See, for example, European patents EP 214,530, 170,915 and 554,765. The catalytic systems obtained, however, either for the support, other than zirconia, or for the choice of promoters, have proved to be ineffective, in terms of conversion and selectivity, in the selective hydrogenation reaction.

The present invention is described in the claims which are also an integral part of the present description.

Therefore, the object of the present invention is a catalyst suitable for the selective hydrogenation of aromatic or polyunsaturated compounds comprising a zirconia support (ZrO2) containing ruthenium, as catalyst, and iron oxide (Fe2O3), as promoter, characterized in that on the support there is present as a further promoter at least one oxide of a metal selected from those of groups IB, IIB and IIIA.

Preferred promoting metals according to the present invention are copper, zinc and gallium, present as CuO, ZnO, Ga2O3. Particularly preferred are the gallium-zinc and copper-zinc pairs.

In particular, the ruthenium content in the solid catalytic system varies from 20 to 55% by weight, with respect to the weight of the zirconia support, while the promoters are present in quantities between 2 and 20% by weight, with respect to the metallic ruthenium. The molar ratios between the promoters are substantially unitary or range from 0.5 to 1.5.

Aromatic compounds which can be selectively hydrogenated by means of the catalyst object of the present invention are benzene, toluene, xylenes, phenol, biphenyl, bisphenol-A, naphthalene, anthracene, etc.

Polyunsaturated compounds which can be selectively hydrogenated by means of the catalyst object of the present invention are dienes, such as 1,3-butadiene or isoprene, or Î ±, β-unsaturated carbonyl compounds such as acrolein, methyl methacrylate, methyl acrylate, ethyl acrylate, butyl, 1,3-butene-2-one, acrylamide, acrylonitrile, etc.

Favorite product is benzene.

The ruthenium-based catalyst object of the present invention can be prepared by precipitating in succession the hydrolyzable salts of the individual metals. In particular, a zirconium alcoholate, for example Zr (OPr) 4, is charged in an aqueous solution of an alkali metal hydroxide, for example KOH, in i-propanol, which, under stirring, forms zirconia which precipitates in the form of finely divided solid. Then, the hydrolyzable salts of the promoting agents are fed, which precipitate as oxides, and lastly the solution of a hydrolyzable salt of ruthenium, for example a Ru halide, always under stirring.

The solution / dispersion thus obtained is heated to a temperature between 50 and 100 ° C and then transferred to an autoclave where it is kept at a temperature between 120 and 180 ° C and a hydrogen pressure between 3 and 6 MPa, always under agitation.

At the end of the treatment, the precipitated solid is recovered by centrifugation.

The catalyst object of the present invention can be used in the selective hydrogenation of aromatic or polyunsaturated compounds, for example in the selective hydrogenation of benzene to cyclohexene. Therefore, a further object of the present invention is a process for the selective hydrogenation of aromatic or polyunsaturated compounds which comprises:

the. loading in an aqueous solution containing from 5 to 15% by weight of an alkaline hydroxide, preferably potassium hydroxide, a heterogeneous catalyst comprising a zirconia support containing ruthenium and an iron oxide promoter (Fe2O3) as catalytic system;

ii. loading the aromatic or polyunsaturated compound into the aqueous solution, while stirring;

iii. reacting the dispersed aromatic or polyunsaturated compound with a continuous flow of hydrogen;

iv. recovering at the end of the reaction the selectively hydrogenated compound by demixing the organic phase from the liquid phase and distillation of the organic phase, characterized in that the heterogeneous catalyst comprises a further promoter selected from at least one oxide of a metal selected from those of groups IB, IIB and IIIA.

According to this further aspect of the present invention, the selective hydrogenation process of aromatic compounds, such as benzene, or polyunsaturated compounds is carried out in an autoclave at a temperature of between 120 and 180 ° C and a pressure of between 4 and 6 MPa. Under these conditions, in order to maximize the yield, for example, in cyclohexene and minimize the yield, for example, in cyclohexane, the reaction times are preferably between 40 and 80 minutes.

In order to put the present invention into practice and better illustrate it, some illustrative and non-limiting examples are reported below.

Example 1

In a 250 mL conical flask 40 mL of 10% KOH solution is then added rapidly under stirring 1 mL of 70% Zr (OPr) 4 in i-PrOH. The formation of ZrO2Ã is practically immediate. The suspension is left under stirring for a few minutes. 10 mL of a 4% FeCl3 <.> 7H2O solution are then added rapidly and in sequence, then 10 ml of H2O with 60 mg of Ga2 (SO4) 3 <.> H2O, (M1), and finally 10 ml of a solution of ZnSO4 <.> H2O, (M2), at 0,6%. A solution of RuCl3 (10 mL at 3.2% as Ru) is added to the suspension, under vigorous stirring. Still under stirring, the suspension is brought to a temperature of 80 ° C, by means of a thermostated oil bath.

Stirring and heating are stopped and the solid is left to cool and settle. Subsequently, the supernatant liquid is eliminated. The solid is dispersed in distilled water and transferred to an autoclave. The reactor is pressurized with 4 MPa of H2e brought to the temperature of 150 ° C. The system is left under these conditions of temperature and pressure under mechanical stirring for 1 h, then cooled to room temperature. The autoclave is depressurized and the solid is separated from the liquid by centrifugation and dried under vacuum. From this preparation about 0.9 g of catalyst at 40% of Ru were obtained and stored in a desiccator.

A semi-continuous reactor (autoclave) was used for the benzene hydrogenation tests. The agitation is ensured by a self-aspirating turbine connected to a magnetic drive system. The thermostating of the reactor is ensured by an oil bath, equipped with a temperature regulation system, directly connected to a thermoresistance placed inside the reactor itself. The benzene is loaded by introducing it from a thermostated loading autoclave at the reaction temperature.

In a typical experiment, 40 ml of aqueous solution of ZnSO4 <.> 7H2O at 18% and 120 mg of Ru-based catalyst, as previously prepared, are loaded into the reactor. The benzene is placed in the loading autoclave and the whole system is purified from the air with N2, then with H2e pressurized to 3 MPa of H2. The temperature of the autoclaves is then brought to 150 ° C and the pressure rises to about 4 MPa. The pressure in the reaction autoclave is brought to 5 MPa and the two autoclaves are put in communication. The benzene flows rapidly into the main reactor and then a stirring speed of 1500 rpm is imposed. The reactor pressure is kept constant by a pressure regulator.

The reaction kinetics are followed by sampling the organic phase. Sampling is performed by stopping the stirring and the sample is analyzed by gas chromatography.

Figure 1 shows the kinetics relating to the catalyst of the example previously prepared Ru / ZrO2 / Fe2O3 / Ga / Zn-KOH

Example 2

We operate as in example 1 but instead of 60 mg of Ga2 (SO4) 3 <.> H2O, 60 mg of CuSO4 <.> 5H2O (M1) are added.

Example 3

We operate as in example 1 except that the solution of ZnSO4 is not added (M2 is missing).

Example 4

We operate as in example 3 (M2 is missing) but instead of 60 mg Ga2 (SO4) 3 <.> H2O, 60 mg of CuSO4 <.> 5H2O (M1) are added.

Example 5

We operate as in example 4 but instead of 60 mg Ga2 (SO4) 3 <.> H2O, 60 mg of ZnSO4 <.> 5H2O (M1) are added.

Example 6

We operate as in example 4 but Ga2 (SO4) 3 <.> H2O is not added (M1 and M2 are missing)

Table 1 below shows the results of the activity and selectivity of the Ru-based catalysts in the hydrogenation of benzene to cyclohexene. Reaction conditions: T 150 ° C, P 50 bar, benzene 40 ml, solution ZnSO40.6 mol L <-1> 40 ml, catalyst 120 mg.

Table 1

Ex. Catalyst M1 M2 Kinetics r0 Selectivity Yield 1 Ru / ZrO2 / Fe / Ga / Zn KOH Ga Zn 7.6 82 47 2 Ru / ZrO2 / Fe / Ga / Cu KOH Cu Zn 6.4 79 44 3 Ru / ZrO2 / Fe / Ga KOH Ga - 7.9 78 41 4 Ru / ZrO2 / Fe / Cu KOH Cu - 4.2 79 45 5 Ru / ZrO2 / Fe / Zn KOH Zn - 6.3 83 46 6 Ru / ZrO2 / Fe KOH - - 6.2 70 40 r0 = 10 <2> mol L <-1> s <-1> gcat <-1>

Claims (14)

CLAIMS 1. Catalyst suitable for the selective hydrogenation of aromatic or polyunsaturated compounds comprising a zirconia (ZrO2) support containing ruthenium, as catalyst, and iron oxide (Fe2O3), as promoter, characterized by the fact that it is present on the support as a further promoter at least one oxide of a metal selected from those of groups IB, IIB and IIIA. 2. Catalyst according to claim 1, wherein the promoting metals are selected from copper, zinc and gallium, present as CuO, ZnO, Ga2O3. 3. Catalyst according to claim 1 or 2, based on ZrO2 / Ru / Fe / Ga / Zn. 4. Catalyst according to claim 1 or 2, based on ZrO2 / Ru / Fe / Cu / Zn. 5. Catalyst according to any one of the preceding claims, wherein the ruthenium content varies from 20 to 55% by weight, with respect to the weight of the zirconia support. 6. Catalyst according to any one of the preceding claims, in which the promoters are present in quantities ranging from 2 to 20% by weight, with respect to the metallic ruthenium. 7. Catalyst according to any one of the preceding claims, in which the molar ratios between the promoters are substantially unitary or range from 0.5 to 1.5. 8. Process for the preparation of the ruthenium-based catalyst according to any one of the preceding claims, which comprises the sequential precipitation of the hydrolyzable salts of the individual metals in an aqueous solution of an alkali metal hydroxide. 9. Process according to claim 8, which comprises the precipitation in an aqueous solution of KOH, under stirring, of a zirconium alcoholate which precipitates in the form of finely divided ZrO2, then the hydrolyzable salts of the promoting agents and finally the hydrolyzable salt of the ruthenium. 10. Process according to claims 8 or 9, in which the solution / dispersion is heated to a temperature between 50 and 100 ° C and then transferred to an autoclave where it is maintained at a temperature between 120 and 180 ° C and a pressure between 3 and 6 MPa, always under stirring. 11. Process for the selective hydrogenation of aromatic or polyunsaturated compounds which includes: the. loading in an aqueous solution containing from 5 to 15% by weight of an alkaline hydroxide a heterogeneous catalyst comprising a zirconia support containing ruthenium and an iron oxide (Fe2O3) promoter as catalytic system; ii. loading the aromatic or polyunsaturated compound into the aqueous solution, while stirring; iii. reacting the dispersed aromatic or polyunsaturated compound with a continuous flow of hydrogen; iv. recovering at the end of the reaction the selectively hydrogenated compound by demixing the organic phase from the liquid phase and distillation of the organic phase. characterized in that the heterogeneous catalyst comprises a further promoter selected from at least one oxide of a metal selected from those of groups IB, IIB and IIIA. 12. Process for the selective hydrogenation of aromatic or polyunsaturated compounds according to claim 11, wherein said selective hydrogenation is carried out at a temperature comprised between 120 and 180 ° C and at a pressure comprised between 4 and 6 MPa. 13. Process for the selective hydrogenation of aromatic or polyunsaturated compounds according to claim 11 or 12, wherein benzene is the aromatic compound to be selectively hydrogenated to cyclohexene. 14. Process for the selective hydrogenation of aromatic or polyunsaturated compounds according to claim 13, wherein, to maximize the cyclohexene yield and minimize the cyclohexane yield, the reaction times are between 40 and 80 minutes.